How do you know if you have a stem cell?

November 19, 2008 3:06 PM

How do you know if you have a stem cell?

I'm reading about scientists turning adult cells into stem cells. How do they know that they have a stem cell?

posted by mpls2 to science & nature (7 comments total)

I guess they'd test it in a lab and see if it did stem-celly stuff?

Some information on the characteristics of stem cells.

Adult stem cells.
posted by turgid dahlia at 3:15 PM on November 19, 2008

Wikipedia says 'stem cells can be isolated based on a distinctive set of cell surface markers'
posted by le morte de bea arthur at 3:18 PM on November 19, 2008

The key feature of a stem cell is that it be pluripotent - capable of differentiating into any other cell type. The definitive way to show this is to inject your putative stem cell into a early stage developing embryo (a blastocyst) and then look at the resulting animal. A true stem cell will contribute to all the tissues in the body. Obviously you can only do this test on non-human stem cells; it would be unethical to do the same experiment with human cells.

A related test is to inject the putative stem cell into an immunodeficient mouse and see if it forms a teratoma - a tumor which contains many different tissue types.

I am a biologist, but not a stem cell biologist. The stem cell page at the NIH linked above is a good resource.
posted by pombe at 3:27 PM on November 19, 2008

If I remember my tissue engineering courses correctly, the core things that you have to establish are pluripotence- that is, by giving your stem cell various stimuli, you can turn it into multiple other types of 'adult' cells- and the ability of the cell to keep dividing without making this commitment. The cell surface markers lmba refers to above are helpful for identification but do not necessarily contribute to these underlying functions; transformed 'adult' stem cells may not express them but still have the right machinery.
posted by monocyte at 3:32 PM on November 19, 2008

Wasn't there an article on the blue not too long ago about how menstrual blood is chock-full-o-stemmies?
posted by TomMelee at 4:09 PM on November 19, 2008

What pombe (and monocyte) talk about is an embryonic stem cell - only embryonic stem cells have these characteristics, which is why they are so coveted by biologists. (TomMelee must be talking about adult stem cells). The most basic definition of a stem cell is a cell that can self renew and differentiate into another cell type. Adult neural stem cells, for example, can make 1) more neural stem cells, and 2) olfactory and hippocampal neurons (so you can remember and smell). But they cannot make the neurons lost in Parkinson's disease, nor many of the neuron types that die in specific diseases.

It is important to make the embryonic versus adult stem cell distinction. Most stem cell biologists would prefer not to use embryonic stem cells because we have to differentiate them into the tissue we want before using them (such as making them neural before trying to make them specific neurons). However, we have to use them if we'd like to make specific neuron types that cannot be made with adult neural stem cells - and that is basically every type of neuron (except the olfactory and hippocampal named above). There may be ways to retrain adult neural stem cells, but they aren't well studied and aren't well accepted by most in the field.
posted by SciGuy at 5:03 PM on November 19, 2008

Cells that are not pluripotent but only multipotent may also be referred to as stem cells; the terminology is still in flux.

I work with adult cells that have been called mesenchymal stem cells, multipotent stromal cells, and bone-marrow-derived progenitor cells (and most permutations of these terms). Their "stemness" is confirmed by causing them to differentiate down various lineages--adipogenic (forming fat cells), osteogenic (bone cells), chondrogenic (cartilage cells)--via chemical cues. (Recent research indicates that mechanical cues can also influence differentiation.) The resulting differentiated cultures are often identified by staining and protein analysis. But these multipotent cells couldn't form another human or even an arbitrary tissue such as blood; the possible pathways are limited.

Obviously, it's inconvenient to go down a differentiation pathway (which takes weeks in culture) just to identify stem cells, so chemical surface proteins are used as identifying markers. These proteins can be tagged with selective fluorescent molecules and used to separate stem cells in a process fluorescence-activated cell sorting (FACS).

In my lab, I'm working on a way to identify stem cells without even tagging them with fluorescent labels, which are undesirable if you want to re-implant the cells for therapeutic purposes. I'm using an optical technique (optical stretching) to see if they can be identified by their mechanical compliance alone; that is, by their "squishyness." If stem cells are stiffer or softer than the surrounding cells, then this technique could be of great use in separating them without having to differentiate them or tag them.
posted by Mapes at 5:07 PM on November 19, 2008 [2 favorites has favorites]